Composition for producing coatings on refractory articles and articles coated therewih



ross Reference WILICIAM ROY MOTT. OF LAKEWOOD, OHIO, ASSIGNOR TO NATIONAL CARBON COMPANY, INC. A CORPORATION OF NEW YORK.

COMPOSITION FOR PRODUCING COATINGS OlN REFRACTORY ARTICLES AND ARTICLES COATED THEE EWITH.

To all when: 2"

The invention also prises refractory articles provided with protective coatings.

Carbon sa very ilesirable element for refractory articles on account oi its extremely high vaporization point, Unfortunately. however, carbon very readily combines with oxygen ei'en at fairly moderate temperatures. and therefore eombusticai readily takes place in oxygerrcontaming atmospheres unless some protecting: means is employecl to art-vent the oxygen reaching the carbon. lor this reason various coati have been proposed tor the carbon retractory articles. but as far as l am aware. none. of them hoe been satisfactory at temperatures in the neighborhood of iraoo i. or inore.

I have found that a very ctliciont protect ing means my beobtained by coating a carbon or graphite article with a mixture of horic oxide (B ilt-ii and compounds oi" iron and chromiu. such as the oxides i'or example. ".lha protecting action of boric oxide alone good up to 1500* as the mol ten oxide eadily wcts either cold or incandcsrer. arbor: and iioivs evenly over its surface. horic oxide-irun-chromium mixture. lheiri'orc protects the carbon art-ielc chioiiy' thcroug'h the horic oxide up to 1500 (.2 although the oxides of iron and chromium are reduced by the carbon to metallic. iron and chromium below this term peraturc. which fill!!! an alloy that is very resistant to oxidation and which tends to form a dense coating on the carbon. Therefore the iron and chromium aid boric oxide in the protecting action up to 15300 and somewhat above this temperature the borio oxide partly vzrporizcs. leaving the partly molten alloy which contains chiefly iron.

Speeifica tion of Letters Patent.

*atvntod .\u". 15. 1922.

Application filed January 14, 1919. Serial No. 271,123.

chromium carbide and boron carbide. as a thin coating on the exterior part of the can hon. This molten coating also wets the carbon and prevents the oxygen from reaching the carbon.

At temperatures in the neighborhood of .1700 P. the iron and chroinuim probably unite with the carbon to form a double carhide in the form oi a dense. impervious coat-- ing which I have found to protect the carbon at temperatureseven ashigh as 3000 C. It therefore will be apparent that. the boric oxide-iron-chromium glaze or coatingwill protect the carbon article. to any temperature up to 3000 H the carbon article has once been raised to a temperature above 1:500 so that the double. carbide !S formed. and is afterwards used at tempera turcs below 1T00 the protecting action is still obtained. a the double carbide coatingwill protect at the lower temperatures as well as atthc higher ones.

There are various ways of applying the coating to carbon articles. one of which is to dissolve the oxides of iron and chromium in molten boric oxide and then dip the cold or hot carbon article therein. on removal the article will be coated with an adherent glaze that will protect it in themanner previously explained.

An alternative method is to paint a mixture of the three oxides. with some temporary binder such as sodium silicate or sugar solution. directly onto the carbon article. and then bake the article sutliciently to form a glaze. 'lhc halting, however. may be accomplished by the heat to which the article is suhiectediu use.

till another method is to mix the three o: .ideswith the carbon forming; the retractory article. so that on heating. the. glaze will be formed on the exterior portion. This method will be especially desirable in forming resistor blocks or rods. as the oxides will aid in producinc the desired resistance. carbon being in many cases of too high a eomluctivity.

While l have mentioned the use of the 0xides in tho protecting: coating. variousequivalents may be substituted. For instance sodium boratc. metallic iron and chromium. as well as the salts oi these clci-ncuts. may be employed. although the lower cost would make it desirable to use the oxides as previ- Search Room ously set forth. There is no particular proportion of the materials that is necessary, but good results may be obtained by coating the arbon article with a glaze consisting J LQ to 6 parts boric oxide, 1 to 3 parts iron oxide and 2. to 6 parts chromimn oxide. If the oxides are homogeneously mixed with the carbon the proportions may be as follows: boric oxide. 2 to 10; iron oxide, 1 to 10 chromium oxide, 2 to with sufiicient carbon to make up 100 parts, for example. The oxides need not be homogeneously mixed with the carbon, but may be mixed therewith only on the outer surface, the

mixture being pasted on the article, or the June 3, 1881.

coating and electrode body may be forced together by extrusion in a well known way, for example as is disclosed in the French patent to Mignon and Rouart. No. 143.206, In case the carbon is mixed with the oxides, even as a homogeneous mixture or as a thin shell, a tar or pitch binder may be used as is usual in forming carbon articles, which on baking will be conver d into coke and act as the binding meansf 80 bricks. etc-., that are adapted to oxidize or react with the surrounding medlum on be- It will be apparent from the foregoing discription that the invention is not limited to carbon articles but may be used in connection with other articles such as resistors,

ing, heated. In the coating is to contam the carbides of the metals, an appropriate mixture of carbon and the oxides of l. boron, iron and chromium in any desired combination may be used.

Haring described my invention, what I claim is: I

1. As a ne article of manufacture, a refractory article provided with a coating comprising an oxy-compound of boron, as sociated with iron and chromium.

2. As a new article of manufacture, a refractory article provided with a coatingcomprising an oxy-compound of boron. as sociated with oxids of iron and chromium.

3. As a new article of manufacture, a carbon article provided with a coating comprising an oxy-compound of boron, associated with iron and ClllOlIlllUl'l.

at. As a new article of manufacture, a carbon article provided with a coating cone prising an oxycompound of boron. associated with oxids of iron and chromium.

A protective coating composition for carbon articles, said composition containing, a component which is fusible at a temperature below the oxidation temperature of carbon in air, and which in the fused state readily wets carbon surfaces or forms a film thereon, said composition also yielding, at a higher tempe 'ature range, a proteetire residue or: reaction product upon the carbon surface.

In testimony whereof, I hereunto aflix my signature.

WILLIAM ROY M OTT. 

